Combination barb restraint and stent attachment deployment mechanism

ABSTRACT

An aneurysmal repair system that utilizes a modified apex and delivery device is designed for accurate endoprosthesis delivery and deployment. The modified apex utilizes segments that overlap and hold one another down as well as the fixation barbs attached thereto. The delivery device holds or secures at least one section of the apex and may be easily released by retraction of a hold down member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to aneurismal repair devices, and moreparticularly, to devices that facilitate the restraint and selectivedeployment of the cranial end of an aneurismal repair device duringdelivery.

2. Discussion of the Related Art

An aneurysm is an abnormal dilation of a layer or layers of an arterialwall, usually caused by a systemic collagen synthetic or structuraldefect. An abdominal aortic aneurysm is an aneurysm in the abdominalportion of the aorta, usually located in or near one or both of the twoiliac arteries or near the renal arteries. The aneurysm often arises inthe infrarenal portion of the diseased aorta, for example, below thekidneys. A thoracic aortic aneurysm is an aneurysm in the thoracicportion of the aorta. When left untreated, the aneurysm may rupture,usually causing rapid fatal hemorrhaging.

Aneurysms may be classified or typed by their position as well as by thenumber of aneurysms in a cluster. Typically, abdominal aortic aneurysmsmay be classified into five types. A Type I aneurysm is a singledilation located between the renal arteries and the iliac arteries.Typically, in a Type I aneurysm, the aorta is healthy between the renalarteries and the aneurysm and between the aneurysm and the iliacarteries.

A Type II A aneurysm is a single dilation located between the renalarteries and the iliac arteries. In a Type II A aneurysm, the aorta ishealthy between the renal arteries and the aneurysm, but not healthybetween the aneurysm and the iliac arteries. In other words, thedilation extends to the aortic bifurcation. A Type II B aneurysmcomprises three dilations. One dilation is located between the renalarteries and the iliac arteries. Like a Type II A aneurysm, the aorta ishealthy between the aneurysm and the renal arteries, but not healthybetween the aneurysm and the iliac arteries. The other two dilations arelocated in the iliac arteries between the aortic bifurcation and thebifurcations between the external iliacs and the internal iliacs. Theiliac arteries are healthy between the iliac bifurcation and theaneurysms. A Type II C aneurysm also comprises three dilations. However,in a Type II C aneurysm, the dilations in the iliac arteries extend tothe iliac bifurcation.

A Type III aneurysm is a single dilation located between the renalarteries and the iliac arteries. In a Type III aneurysm, the aorta isnot healthy between the renal arteries and the aneurysm. In other words,the dilation extends to the renal arteries.

A ruptured abdominal aortic aneurysm is presently the thirteenth leadingcause of death in the United States. The routine management of abdominalaortic aneurysms has been surgical bypass, with the placement of a graftin the involved or dilated segment. Although resection with a syntheticgraft via a transperitoneal or retroperitoneal procedure has been thestandard treatment, it is associated with significant risk. For example,complications include perioperative myocardial ischemia, renal failure,erectile impotence, intestinal ischemia, infection, lower limb ischemia,spinal cord injury with paralysis, aorta-enteric fistula, and death.Surgical treatment of abdominal aortic aneurysms is associated with anoverall mortality rate of five percent in asymptomatic patients, sixteento nineteen percent in symptomatic patients, and is as high as fiftypercent in patients with ruptured abdominal aortic aneurysms.

Disadvantages associated with conventional surgery, in addition to thehigh mortality rate, include an extended recovery period associated withthe large surgical incision and the opening of the abdominal cavity,difficulties in suturing the graft to the aorta, the loss of theexisting thrombosis to support and reinforce the graft, theunsuitability of the surgery for many patients having abdominal aorticaneurysms, and the problems associated with performing the surgery on anemergency basis after the aneurysm has ruptured. Further, the typicalrecovery period is from one to two weeks in the hospital and aconvalescence period, at home, ranging from two to three months or more,if complications ensue. Since many patients having abdominal aorticaneurysms have other chronic illnesses, such as heart, lung, liverand/or kidney disease, coupled with the fact that many of these patientsare older, they are less than ideal candidates for surgery.

The occurrence of aneurysms is not confined to the abdominal region.While abdominal aortic aneurysms are generally the most common,aneurysms in other regions of the aorta or one of its branches arepossible. For example, aneurysms may occur in the thoracic aorta. As isthe case with abdominal aortic aneurysms, the widely accepted approachto treating an aneurysm in the thoracic aorta is surgical repair,involving replacing the aneurysmal segment with a prosthetic device.This surgery, as described above, is a major undertaking, withassociated high risks and with significant mortality and morbidity.

Over the past five years, there has been a great deal of researchdirected at developing less invasive, endovascular, i.e., catheterdirected, techniques for the treatment of aneurysms, specificallyabdominal aortic aneurysms. This has been facilitated by the developmentof vascular stents, which can and have been used in conjunction withstandard or thin-wall graft material in order to create a stent-graft orendograft. The potential advantages of less invasive treatments haveincluded reduced surgical morbidity and mortality along with shorterhospital and intensive care unit stays.

Stent-grafts or endoprostheses are now Food and Drug Administration(FDA) approved and commercially available. Their delivery proceduretypically involves advanced angiographic techniques performed throughvascular accesses gained via surgical cut down of a remote artery, whichmay include the common femoral or brachial arteries. Over a guidewire,the appropriate size introducer will be placed. The catheter andguidewire are passed through the aneurysm. Through the introducer, thestent-graft will be advanced to the appropriate position. Typicaldeployment of the stent-graft device requires withdrawal of an outersheath while maintaining the position of the stent-graft with aninner-stabilizing device. Most stent-grafts are self-expanding; however,an additional angioplasty procedure, e.g., balloon angioplasty, may berequired to secure the position of the stent-graft. Following theplacement of the stent-graft, standard angiographic views may beobtained.

Due to the large diameter of the above-described devices, typicallygreater than twenty French (3 F=1 mm), arteriotomy closure typicallyrequires open surgical repair. Some procedures may require additionalsurgical techniques, such as hypogastric artery embolization, vesselligation, or surgical bypass in order to adequately treat the aneurysmor to maintain blood flow to both lower extremities. Likewise, someprocedures will require additional advanced catheter directedtechniques, such as angioplasty, stent placement and embolization, inorder to successfully exclude the aneurysm and efficiently manage leaks.

While the above-described endoprostheses represent a significantimprovement over conventional surgical techniques, there is a need toimprove the endoprostheses, their method of use and their applicabilityto varied biological conditions. Accordingly, in order to provide a safeand effective alternate means for treating aneurysms, includingabdominal aortic aneurysms and thoracic aortic aneurysms, a number ofdifficulties associated with currently known endoprostheses and theirdelivery systems must be overcome. One concern with the use ofendoprostheses is the prevention of endo-leaks and the disruption of thenormal fluid dynamics of the vasculature. Devices using any technologyshould preferably be simple to position and reposition as necessary,should preferably provide an acute, fluid tight seal, and shouldpreferably be anchored to prevent migration without interfering withnormal blood flow in both the aneurysmal vessel as well as branchingvessels. In addition, devices using the technology should preferably beable to be anchored, sealed, and maintained in bifurcated vessels,tortuous vessels, highly angulated vessels, partially diseased vessels,calcified vessels, odd shaped vessels, short vessels, and long vessels.In order to accomplish this, the endoprostheses should preferably behighly durable, extendable and re-configurable while maintaining acuteand long-term fluid tight seals and anchoring positions.

The endoprostheses should also preferably be able to be deliveredpercutaneously utilizing catheters, guidewires and other devices whichsubstantially eliminate the need for open surgical intervention.Accordingly, the diameter of the endoprostheses in the catheter is animportant factor. This is especially true for aneurysms in the largervessels, such as the thoracic aorta. In addition, the endoprosthesesshould preferably be percutaneously delivered and deployed such thatsurgical cut down is unnecessary.

Many aneurismal repair devices currently in the market utilize a wovenDacron® graft material and a metallic stent or scaffold. Typically, thestents are attached to the graft material by sutures. Even though thestents are sutured in place, this does not completely eliminate relativemovement between the stent and the graft material caused by thepulsatile movement of the blood in the particular artery and themovement of the artery itself. This relative motion between the stentand the graft causes wear and potentially a separation or openingbetween the graft and the stent. This potential separation or openingmay in turn lead to endo leaks. Accordingly, it would be highlyadvantageous to develop a system for preventing this or substantiallyeliminating relative movement between the stent and the graft.

Many aneurismal repair devices have deployment systems that address twosignificant concerns individually or not at all. The two significantconcerns are accurate stent deployment and fixation barb restraint.Accordingly, a design is needed to allow for the restraint and selectivedeployment of the cranial end of an endoprosthesis during delivery whilealso restraining the fixation barbs from deploying before the prosthesishas centered itself in the target vessel during deployment.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages associated withcurrently utilized aneurismal repair devices.

In accordance with one aspect, the present invention is directed to ananeurysm repair system. The repair system comprises at least onesubstantially cylindrical stent segment, the at least one substantiallycylindrical stent segment having modified apexes, the modified apexesincluding first sections, second sections and fixation barbs, the secondsections being configured to overlap and restrain the fixation barb onan adjacent apex, and graft material affixed, via attachment elements,to at least a portion of the at least one substantially cylindricalstent segment.

In accordance with another aspect, the present invention is directed toa stent. The stent comprising at least one substantially cylindricalstent segment having modified apexes, the modified apexes includingfirst sections, second sections and fixation barbs, the second sectionsbeing configured to overlap and restrain the fixation barb on anadjacent apex.

In accordance with yet another aspect, the present invention is directedto a stent system. The stent system comprising at least onesubstantially cylindrical stent segment having modified apexes, themodified apexes including first sections, second sections and fixationbarbs, the second sections being configured to overlap and restrain thefixation barb on an adjacent apex, and a securing mechanism having atleast one protruding member configured for placement in at least one ofthe second sections and a hold down member connected on one end to theat least one protruding member and on the other end to a pull backmechanism.

The present invention is directed to a combination barb restraint andstent deployment mechanism. The exemplary stents of the presentinvention include modified apexes wherein one section of the modifiedapex holds down the fixation barbs on an adjacent apex. With thisdesign, the proximal end of an endoluminal prosthesis may be restrainedwith one or more fingers attached to a member that is pulled free fromthe assembly when the device is deployed.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the invention will beapparent from the following, more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

FIG. 1 is a diagrammatic representation of the exemplary anchoring andsealing prosthesis in accordance with the present invention.

FIG. 2 is a diagrammatic representation of an exemplary anchoring andsealing prosthesis with no graft material and/or stitching in certainlocations in accordance with the present invention.

FIG. 3 is an elevational view of an endovascular graft in accordancewith the present invention.

FIG. 4 is a perspective view of an expanded stent segment of theendovascular graft in accordance with the present invention.

FIG. 4A is a fragmentary perspective view of a portion of the stentsegment of FIG. 4.

FIG. 4B is a fragmentary perspective view of a portion of the stentsegment of FIG. 4.

FIG. 4C is an enlarged plan view of a section of the stent segment ofFIG. 4.

FIG. 4D is an enlarged plan view of a section of the stent segment ofFIG. 4.

FIG. 5 is a perspective view of another expanded stent segment of theendovascular graft in accordance with the present invention.

FIG. 6 is an elevational view of an endovascular graft in accordancewith the present invention.

FIG. 7 is a diagrammatic representation of a stent segment having afirst modified apex design in accordance with the present invention.

FIGS. 8A and 8B are diagrammatic representations of a portion of themodified apex as it is attached to the graft material in accordance withthe present invention.

FIG. 9A is a diagrammatic presentation of a modified graft in accordancewith the present invention.

FIG. 9B is a diagrammatic representation of a modified stent-graft inaccordance with the present invention.

FIG. 10 is a diagrammatic representation of a stent segment having asecond modified apex design in accordance with the present invention.

FIG. 11 is a diagrammatic representation of a stent segment having athird modified apex design in accordance with the present invention.

FIG. 12 is a diagrammatic representation of a stent segment having afourth modified apex design in accordance with the present invention.

FIG. 13 is a first diagrammatic representation of a modified apex andfixation barb in accordance with the present invention.

FIG. 14 is a second diagrammatic representation of a modified apex andfixation barb in accordance with the present invention.

FIG. 15 is a third diagrammatic representation of a modified apex andfixation barb in accordance with the present invention.

FIG. 16 is a diagrammatic representation of a stent deployment systemfor the modified apexes in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is illustrated an exemplary embodiment of ananchoring and sealing component 100 of an aneurysm repair system. Theanchoring and sealing component 100 comprises a trunk section 102 and abifurcated section, including two legs 104, 106. Graft material 108,described in detail below, is affixed to at least a portion of the trunksection 102 and to all of the legs 104, 106. The graft material may beattached via any number of means. In the exemplary embodiment, the graftmaterial 108 is attached to various portions of the underlying structureby sutures 110. As illustrated, the graft material 108 is affixed with acontinuous stitch pattern on the end of the trunk section 102 and bysingle stitches elsewhere. It is important to note that any stitchpattern may be utilized, and other devices, such as staples, may beutilized to connect the graft material 108 to the underlying structure.The sutures 110 may comprise any suitable biocompatible material that ispreferably highly durable and wear resistant.

The underlying structure of the trunk section 102, as illustrated inFIG. 2, comprises a substantially tubular stent structure or latticecomprising multiple stent sections. The stent or lattice structurecomprises a single row of substantially diamond shaped elements 112 onone end, multiple rows of substantially diamond shaped elements 114 onthe other end, a plurality of longitudinal struts 116 and a single,substantially zigzag shaped stent element 117. The plurality oflongitudinal struts 116 are connected to the apexes of the substantiallydiamond shaped elements 114. The single, substantially zigzag shapedstent element 117 comprises a number of barbs 119 protruding therefromfor anchoring the device in the vessel to be repaired. This exemplaryembodiment may be utilized for anchoring and sealing in positionswherein there are branches off the main artery. For example, thisexemplary embodiment may be utilized for supra-renal anchoring.Accordingly, the graft material 108 is only attached below thelongitudinal struts 116 so that blood may flow into the renal arteriesfrom the aorta. Infra-renal designs are also possible.

The underlying structure of the bifurcated section, as illustrated inFIG. 2, comprises a plurality of individual, substantially tubular stentelements 118. Each stent element 118 comprises a substantially zigzagpattern. As illustrated, leg 104 comprises three stent elements 118 a,118 b, 118 c and leg 106 comprises two stent elements 118 d, 118 e. Asillustrated, in this exemplary embodiment, the stent elements do notline up and the legs are of two different lengths. This exemplary designallows for nesting of the legs 104, 106 such that the profile of thedevice is reduced.

In order to compensate for the missing stent elements, the legs areconnected at the bifurcation as illustrated in FIG. 1. The legs 104, 106may be connected in any suitable manner. In the exemplary embodiment,the two legs 104, 106 are connected by suturing them together. Thesutures 120 connect the graft material 108 on each leg 104, 106together. The sutures may be non-biodegradable or biodegradable.Biodegradable sutures would dissolve over time thereby allowing the twolegs to move independently.

Referring now to FIG. 3, there is illustrated an exemplary embodiment ofan endovascular graft 300 of an aneurysm repair system. The exemplaryendovascular graft 300 comprises one or more first stent segments 310,one second stent segment 320 and a third stent segment 330. In a typicaluse scenario, the third stent segment 330 would be anchored in healthytissue below the aneurysm and the uppermost first stent segment 310would be in fluid communication with the anchoring and sealing component100. The second stent segment 320 comprises a tapered profile, having adiameter at one end equal to that of the first stent segment 310 and adiameter at the other end equal to that of the third stent segment 330.The length of the endovascular graft 300 may be adjusted by varying thenumber of first stent segments 310 utilized.

FIG. 4 is a detailed perspective view of an exemplary embodiment of thethird stent segment 330. The third stent segment 330 comprises aplurality of struts 332 connected in a substantially zigzag pattern. Asillustrated, the exemplary third stent segment 330 comprises three setsof zigzag-connected struts 332, thereby forming substantiallydiamond-shaped cells. The non-connected apex 334 of each diamond shapedcell, illustrated in greater detail in FIG. 4A, comprises a smooth,uniform width curved region formed at the intersection of two struts 332of each diamond-shaped cell. This shape is cut directly into the stentsegment 330 during the initial machining steps, typically laser cutting,and is maintained during all subsequent finishing processing. Thejunctions 336 between the zigzag-connected struts 332, illustrated ingreater detail in FIG. 4B occurs at the intersection of four struts 332.Preferably, each junction 336 of four struts 332 comprises twoindentations 338 and 340 as illustrated in FIG. 4B.

The regions proximate the non-connected apexes 334 and the junctions 336are generally the highest stress regions in the third stent segment 330.To minimize the stresses in these regions, these regions are designed tomaintain uniform beam widths proximate where the struts 332interconnect. Beam width refers to the width of a strut junction 336.Indentations 338 and 340 are cut or machined into the junctions 336 tomaintain a uniform beam width in this area, which is generally subjectto the highest stress. Essentially, by designing the junctions 336 tomaintain uniform beam widths, the stress and strain that would normallybuild up in a concentrated area, proximate the junction 336, is allowedto spread out into the connecting regions, thereby lowering the peakvalues of the stress and strain in the stent structure.

To further minimize the maximum stresses in the struts 332 of the thirdstent segment 330, the struts 332 may have a tapering width. Forexample, in one exemplary embodiment, the struts 332 may be designed tobecome wider as it approaches a junction 336. FIG. 4C is an enlargedpartial view of the third sent segment 330 in its expanded conditionswhich illustrates the tapering width of the struts 332. In thisexemplary embodiment, the strut 332 proximate the junction 336 (width a)is about 0.025 cm and gradually tapers to a dimension of about 0.0178 cmin the mid-region of the strut 332 (width b). By tapering the struts'widths, the stresses in the struts 332 adjacent the junction 336 isspread out away from the junction 336. The tapering of the struts 332 isaccomplished during the machining of the tube of material from which thestent 330 is cut. However, by tapering the struts 332 in this manner,there is a tradeoff. The stent segment 330 becomes somewhat lessresistant to localized deformations, caused for example, by a protrusionwithin the vessel lumen. This localized deformation may lead to a localtorsional loading on some of the struts 332, and, therefore, since thestruts 332 in this exemplary embodiment have a relatively significantportion of their length with a reduced width, their torsional rigidityis reduced.

If maximizing the resistance to localized deformation is preferred, thestruts 332 may be maintained at a uniform width, or more preferably havea reverse taper, as illustrated in FIG. 4D, wherein the width at point ais less than the width at point b. In this exemplary embodiment, thereverse taper struts 332 are about 0.025 cm proximate the junction 336and about 0.028 cm in the central region of the struts. While thisreverse taper tends to increase the stresses somewhat proximate thejunctions 336, this increase is very small relative to the decrease instresses gained by having the side indentations 338, 340 illustrated inFIG. 4B, as well as the uniform width connections illustrated in FIG.4A. In addition, since the reverse taper serves to increase thetorsional rigidity of the strut 332, the stent structure resists localdeformation and tends to maintain a substantially circularcross-sectional geometry, even if the lumen into which the stent ispositioned in non-circular in cross-section.

In a preferred exemplary embodiment, the third stent segment 330 isfabricated from a laser cut tube, of initial dimensions 0.229 cm insidediameter by 0.318 cm outside diameter. The struts 332 are preferably0.0229 cm wide adjacent the four strut junctions 336 and six mm long,with a reverse taper strut width. Also, to minimize the number ofdifferent diameter combination of grafts systems, it is preferred thatthe third stent segment 330 have an expanded diameter of sixteen mm.Similarly, the proximal portion of the graft material forming the legsis flared, having a diameter of sixteen mm. This single diameter for thethird stent segment of the graft system would enable its use in arterieshaving a non-aneurysmal region of a diameter from between eight andfourteen mm in diameter. It is also contemplated that multiple diametercombinations of third stent segment 330 and graft flare would bedesirable.

Referring back to FIG. 3, the one or more first stent segments 310 arealso formed from a shape set laser cut tube, similar to the third stentsegment 330 described above. The one or more first stent segments 310comprise a single circumferential row of zigzag or sinusoidally arrangedelements. In the exemplary embodiment illustrated in FIG. 3, and ingreater detail in FIG. 5, the first stent segment 310 comprises tenzigzag or sinusoidal undulations. The one or more first stent segments310 are formed with uniform width connections at the intersections 314of the struts 312 forming the zigzag or sinusoidal pattern. The one ormore first stent segments 310 are preferably cut from tubing having aninside diameter of 0.251 cm and an outside diameter of 0.317 cm. Thestrut widths are preferably about 0.33 cm wide adjacent strutintersections 314 and the struts 312 are preferably seven mm long andthe one or more first stent segments 310 are preferably eleven mm indiameter when expanded.

The second stent segment 320 comprises a tapered profile, having adiameter at one end which is the same as the one or more first stentsegments 310, and a diameter at the other end matching the diameter ofthe third stent segment 330. The second stent segment 320 is identicalto the one or more first stent segments 310 except for the taper.

As is explained in detail subsequently, the stent segments 310, 320 and330 are secured in position by the graft material.

Nitinol is utilized in a wide variety of applications, including medicaldevice applications as described herein. Nitinol or Ni—Ti alloys arewidely utilized in the fabrication or construction of medical devicesfor a number of reasons, including its biomechanical compatibility, itsbiocompatibility, its fatigue resistance, its kink resistance, itsuniform plastic deformation, its magnetic resonance imagingcompatibility, its constant and gentle outward pressure, its dynamicinterference, its thermal deployment capability, its elastic deploymentcapability, its hysteresis characteristics and because it is modestlyradiopaque.

Nitinol, as described above, exhibits shape memory and/or superelasticcharacteristics. Shape memory characteristics may be simplisticallydescribed as follows. A metallic structure, for example a Nitinol tubethat is in an Austenite phase may be cooled to a temperature such thatit is in the Martensite phase. Once in the Martensite, the Nitinol tubemay be deformed into a particular configuration or shape by theapplication of stress. As long as the Nitinol tube is maintained in theMartensite phase, the Nitinol tube will remain in its deformed shape. Ifthe Nitinol tube is heated to a temperature sufficient to cause theNitinol tube to reach the Austenite phase, the Nitinol tube will returnto its original or programmed shape. The original shape is programmed tobe a particular shape by well known techniques. Superelasticcharacteristics may be simplistically described as follows. A metallicstructure, for example, a Nitinol tube that is in an Austenite phase maybe deformed to a particular shape or configuration by the application ofmechanical energy. The application of mechanical energy causes a stressinduced Martensite phase transformation. In other words, the mechanicalenergy causes the Nitinol tube to transform from the Austenite phase tothe Martensite phase. By utilizing the appropriate measuringinstruments, one can determine that the stress from the mechanicalenergy causes a temperature drop in the Nitinol tube. Once themechanical energy or stress is released, the Nitinol tube undergoesanother mechanical phase transformation back to the Austenite phase andthus its original or programmed shape. As described above, the originalshape is programmed by well known techniques. The Martensite andAustenite phases are common phases in many metals.

Medical devices constructed from Nitinol are typically utilized in boththe Martensite phase and/or the Austenite phase. The Martensite phase isthe low temperature phase. A material in the Martensite phase istypically very soft and malleable. These properties make it easier toshape or configure the Nitinol into complicated or complex structures.The Austenite phase is the high temperature phase. A material in theAustenite phase is generally much stronger than the material in theMartensite phase. Typically, many medical devices are cooled to theMartensite phase for manipulation and loading into delivery systems, asdescribed above with respect to stents and then when the device isdeployed at body temperature, they return to the Austenite phase.

The first, second and third stent segments 310, 320, 330 are preferablyself-expandable and formed from a shape memory alloy. Such an alloy maybe deformed from an original, heat-stable configuration to a second,heat-unstable configuration. The application of a desired temperaturecauses the alloy to revert to an original heat-stable configuration. Aparticularly preferred shape memory alloy for this application is binarynickel titanium alloy comprising about 55.8 percent Ni by weight,commercially available under the trade designation NITINOL. This NiTialloy undergoes a phase transformation at physiological temperatures. Astent made of this material is deformable when chilled. Thus, at lowtemperatures, for example, below twenty degrees centigrade, the stent iscompressed so that it can be delivered to the desired location. Thestent may be kept at low temperatures by circulating chilled salinesolutions. The stent expands when the chilled saline is removed and itis exposed to higher temperatures within the patient's body, generallyaround thirty-seven degrees centigrade.

In preferred embodiments, each stent is fabricated from a single pieceof alloy tubing. The tubing is laser cut, shape-set by placing thetubing on a mandrel, and heat-set to its desired expanded shape andsize.

In preferred embodiments, the shape setting is performed in stages atfive hundred degrees centigrade. That is, the stents are placed onsequentially larger mandrels and briefly heated to five hundred degreescentigrade. To minimize grain growth, the total time of exposure to atemperature of five hundred degrees centigrade is limited to fiveminutes. The stents are given their final shape set for four minutes atfive hundred fifty degrees centigrade, and then aged to a temperature offour hundred seventy degrees centigrade to import the proper martensiteto austenite transformation temperature, then blasted, as described indetail subsequently, before electropolishing. This heat treatmentprocess provides for a stent that has a martensite to austenitetransformation which occurs over a relatively narrow temperature range;for example, around fifteen degrees centigrade.

To improve the mechanical integrity of the stent, the rough edges leftby the laser cutting are removed by combination of mechanical gritblasting and electropolishing. The grit blasting is performed to removethe brittle recast layer left by the laser cutting process. This layeris not readily removable by the electropolishing process, and if leftintact, could lead to a brittle fracture of the stent struts. A solutionof seventy percent methanol and thirty percent nitric acid at atemperature of minus forty degrees centigrade or less has been shown towork effectively as an electropolishing solution. Electrical parametersof the electropolishing are selected to remove approximately 0.00127 cmof material from the surfaces of the struts. The clean, electropolishedsurface is the final desired surface for attachment to the graftmaterials. This surface has been found to import good corrosionresistance, fatigue resistance, and wear resistance.

The graft material or component 600, as illustrated in FIG. 6, may bemade from any number of suitable biocompatible materials, includingwoven, knitted, sutured, extruded, or cast materials comprisingpolyester, polytetrafluoroethylene, silicones, urethanes, and ultralightweight polyethylene, such as that commercially available under the tradedesignation SPECTRA™. The materials may be porous or nonporous.Exemplary materials include a woven polyester fabric made from DACRON™or other suitable PET-type polymers.

In one exemplary embodiment, the fabric for the graft material is aforty denier (denier is defined in grams of nine thousand meters of afilament or yarn), twenty-seven filament polyester yarn, having aboutseventy to one-hundred end yarns per cm per face and thirty-two toforty-six pick yarns per cm face. At this weave density, the graftmaterial is relatively impermeable to blood flow through the wall, butis relatively thin, ranging between 0.08 and 0.12 mm in wall thickness.

The graft component 600 is a single lumen tube and preferably has ataper and flared portion woven directly from the loom, as illustratedfor the endovascular graft 300 shown in FIG. 3.

Prior to attachment of the graft component 600 to the stents 310, 320,330, crimps are formed between the stent positions by placing the graftmaterial on a shaped mandrel and thermally forming indentations in thesurface. In the exemplary embodiment illustrated in FIGS. 3 and 6, thecrimps 602 in the graft 400 are about two mm long and 0.5 mm deep. Withthese dimensions, the endovascular graft 300 can bend and flex whilemaintaining an open lumen. Also, prior to attachment of the graftcomponent 600 to the stents 310, 320 330, the graft material is cut in ashape to mate with the end of each end stent.

As stated above, each of the stent segments 310, 320 and 330 is attachedto the graft material 600. The graft material 600 may be attached to thestent segments 310, 320, 330 in any number of suitable ways. In oneexemplary embodiment, the graft material 600 may be attached to thestent segments 310, 320, 330 by sutures.

The method of suturing stents in place is important for minimizing therelative motion or rubbing between the stent struts and the graftmaterial. Because of the pulsatile motion of the vasculature andtherefore the graft system, it is possible for relative motion to occur,particularly in areas where the graft system is in a bend, or if thereare residual folds in the graft material, due to being constrained bythe aorta or iliac arteries.

Ideally, each strut of each stent segment is secured to the graftmaterial by sutures. In an exemplary embodiment, the suture material isblanket stitched to the stent segments at numerous points to securelyfasten the graft material to the stent segments. As stated above, asecure hold is desirable in preventing relative motion in an environmentin which the graft system experiences dynamic motion arising frompulsatile blood pressure, in addition to pulsation of the arteries thatare in direct mechanical contact with the graft system. The stentsnearest the aortic and iliac ends of the graft system (the uppermostfirst stent segment 310 and the third stent segment 330 respectively)are subject to the pulsatile motion arising from direct internalcontact. These struts in particular should be well secured to the graftmaterial. As illustrated in FIG. 6, the stitches 604 on the upper mostfirst stent segment 310 are positioned along the entire zigzagarrangement of struts. The upper and lower apexes of the third stentsegment may be stitched utilizing a similar configuration. It isdifficult to manipulate the suture thread precisely around the strutsthat are located some distance away from an open end, accordingly,various other simpler stitches may be utilized on these struts, or nostitches may be utilized in these areas.

As illustrated in FIG. 6, each of the struts in the first stent segment310 is secured to the graft material 600 which has been cut to match theshape of the stent segment 310. The blanket stitching 604 completelyencircles the strut and bites into the graft material 600. Preferably,the stitch 604 encircles the strut at approximately five equally spacedlocations. Each of the struts on each end of the third stent segment 330is attached to the graft material, which has been cut to make the shapeof the stent segment 330, in the same manner as the first stent segment310.

A significant portion of the graft will not rest directly againstvascular tissue. This portion of the graft will be within the dilatedaneurysm itself. Therefore, this portion of the graft will notexperience any significant pulsatile motion. For this reason, it is notnecessary to secure the stent segments to the graft material asaggressively as the stent structure described above. Therefore, onlypoint stitches 606 are necessary for securing these stents.

It is important to note that a wide variety of sutures are available. Itis equally important to note that there are a number of alternativemeans for attaching the graft material to the stent, including welding,gluing and chemical bonding.

As described above with respect to suturing stents in place, it isimportant to minimize or substantially reduce the relative motion orrubbing between the stent struts and the graft material. This relativemotion arises from pulsatile blood pressure in addition to the pulsationof the arteries that are in direct mechanical contact with the graftsystem.

The present invention is directed to a means for attaching graftmaterial to stent structures in such a manner as to significantly reduceor substantially eliminate this relative motion. The means may beutilized in any of the stent structures described herein, including thestents forming the trunk section and bifurcated section of the anchoringand sealing component of the repair device and the first, second andthird stent segments of the endovascular graft.

Referring to FIG. 7, there is illustrated an exemplary embodiment of amodified stent cell 700 design in accordance with the present invention.As shown, rather than a simple apex 334 as illustrated in FIG. 4, themodified stent cell 700 comprises a more complex or modified apex 702that is designed to more securely attach the graft to the stent whileallowing the graft material to move with the apex as is illustrated inFIGS. 8A and 8B and described subsequently. The modified apex 702comprises a tab like structure 704 and a narrow neck structure 706. Thisconfiguration allows the sutures to be connected utilizing a deltastitch as described in more detail below. This modified apex 702 maycomprise other suitable configurations and sizes so long as it allowsfor securely holding the delta stitch or any other stitch or attachingelements, and does not significantly impact the size of the overalldevice. The modified apex 702 may comprise radiopaque material such astantalum and thus serve a dual role as holder and marker.

Referring now to FIGS. 8A and 8B, there is illustrated the more complexapex 702 relative to the graft material 802 forming the particularcomponent. In both figures, the more complex modified apex 702 issecured to the graft material 802 by any suitable, non-biodegradable ornon-bioerrodable suture material 804 utilizing a delta stitch. The deltastitch is so named because when looked at as a single entity, thestitching pattern forms a substantially delta configuration. Asillustrated, the delta stitch suture 804 fits around two struts 708 andthe narrow neck structure 706. With this configuration, the apex itselfholds two legs of the delta stitch in position, and the combination ofthe narrow neck structure 706 along with the tab 704 holds the third legof the delta stitch in position. It is important to note that any stitchmay be utilized and that if so desired, the stitching material may bemade out of a degradable material. Utilizing a degradable stitchmaterial allows for an acute connection, but also allows for removal ofa component if desired after the material degrades.

As set forth above, this unique arrangement not only holds the graft tothe stent, but also allows for movement of the graft together with thestent, thereby ensuring minimal or substantially no relative movement.The black square 806 of the graft material 802 is always maintained inposition behind the tab 704 even though the stent structure moves andchanges shape. Without this relative movement, wear is reduced.

In an alternative exemplary embodiment, the graft material itself maycomprise openings for securing the more complex apex 702 illustrated inFIGS. 7, 8A and 8B. With this type of configuration, no sutures or otherattachment means or elements may be required. FIG. 9A illustrates asubstantially cylindrical section of graft material 902 comprising aplurality of openings or slits 904. These slits 904 are designed largeenough for the tabs 704 of the stent to go through, but small enough tohold them in place as illustrated in FIG. 9B with the stent struts 708shown in phantom.

With respect to the exemplary embodiment illustrated in FIG. 7, amodified apex having a protrusion was utilized; however, in alternateexemplary embodiments, no protrusion may be required. For example, FIG.10 illustrates a modified apex 1002 having a necked down region 1004 forholding a stitch or other suitable holding device such as a clip orstaple. FIG. 11 illustrates a modified apex 1102 having multiple holes1104 for securing a stitch or other suitable securing devices. In yetanother alternate exemplary embodiment illustrated in FIG. 12, amodified apex 1202 may comprise a series of indents or notches 1204 tohold the attachment means. In each of these exemplary embodiments, thereis no protrusion, just simply an attachment section. In addition,although shown and described as being on every apex, the presentinvention may be utilized on one, every other one or any combination ofapexes.

In accordance with another exemplary embodiment, the present inventionis directed to a modified apex having barbs for anchoring thestent-grafts into position. The barbs may be utilized with any of thestent structures described herein, but are preferably utilized with theanchoring and sealing component 100 illustrated in FIGS. 1 and 2. Morespecifically, the apexes of the substantially diamond shaped elements112 would be modified as illustrated in FIG. 13. However, it isimportant to note that these barbs may be utilized with other cellstructures in addition to diamonds, for example, a simple sinusoidalshape. The description below is only for illustrative purposes. FIG. 13illustrates a modified apex 1300 having a first section 1302, a secondsection 1304 and a fixation barb 1306.

This single modified apex 1300 is illustrated in the non-deployed state.FIG. 14 illustrates two modified apexes 1300 in the unexpanded orundeployed state and lends understanding as to how the invention worksas well as its advantages. With this overlapping configuration of secondsections 1304, the second section 1304 holds down the fixation barb 1306in an adjacent apex. Once the device is deployed and the stent expands,the second sections 1304 no longer overlap thereby freeing the fixationbarbs 1306 to extend outwardly and engage the vessel walls asillustrated in FIG. 15.

In one exemplary embodiment, the fixation barbs 1306 are shape set, asdescribed herein, to angle away from the device for proper vessel wallengagement. In other words, the final configuration of the fixationbarbs 1306 is programmed into the self-expanding alloy and thenrestrained for delivery as is explained in detail subsequently. Inalternate exemplary embodiments, the apexes may be designed to twist ordeform during expansion such that the deformation may be utilized topull the fixation barbs 1306 into its final position thereby eliminatingthe need for shape setting.

This unique apex design offers a number of advantages including reducingthe strain on the apex of the stent, reduced vessel stress due to thewider apex and the prevention of premature fixation barb release. Thestrain on each apex is reduced by opening the angle of the apex. As canbe seen from a comparison of FIGS. 1 and 2 with FIG. 13, the radius ofcurvature of the modified apex is much greater, thereby reducing strainon the apex. Reduced vessel stress is achieved by the increased area ofthe second section 1304 of the modified apex 1300. This increase in areais spread out around the circumference of the vessel. Premature fixationbarb release prevention is achieved by having the fixation barbs 1306restrained during the entire prosthesis deployment and only releasedwhen the proximal or cranial end of the device is released.

FIG. 16 illustrates a stent section having modified apexes 1300 mountedon a delivery device. As illustrated, in the unexpanded or undeployedconfiguration, the second sections 1304 overlap and hold the fixationbarbs 1306 in place. Essentially, the second sections 1304 are atsubstantially right angles to the first sections 1302. In one exemplaryembodiment, the delivery device includes a hold down member thatcomprises a tubular member 1602 that slides coaxially over the innermember of a standard catheter based delivery system. The tubular member1602 comprises a number of protrusions or fingers 1604 at its proximalend that engage the openings of the second sections 1304 and function toprevent them from opening. Essentially, the fingers 1604 are positionedthrough the openings of the second sections 1304.

In operation, once the device is positioned in the proper location, theouter sheath (not shown) is retracted. Once the outer sheath isretracted, last minute positioning of the device may be accomplished.Once positioning is complete, the tubular member 1602 is retracted byany suitable means, such as pull back wires, and the fingers 1604 areremoved from the second members 1304 and thus the device is free toexpand. This simple multi-finger release mechanism may be utilized torestrain all of the proximal apexes. Alternately, due to the overlappingdesign of the apexes, as few as a single finger may be utilized torestrain the entire circumference of the stent.

Accordingly, this unique design allows for the restraint and selectivedeployment of the cranial end of an endovascular prosthesis duringdelivery. It is also desirable to restrain the fixation barbs fromdeploying before the prosthesis has centered itself in the target vesselduring deployment. Other devices have addressed these requirementsindividually. This device addresses both requirements. Essentially, thisinvention provides a means for restraining the cranial end of thesupra-renal portion of an endoprosthesis that also effectively restrainsthe fixation barbs. With this design, the proximal end of the prosthesismay be restrained with one or more fingers attached to a cylindricalmember that is pulled free from the assembly by the operator orphysician in order to initiate the deployment of the proximal portion ofthe stent. It is important to note that if a single finger is utilized,a cylindrical member may not be needed. For example, as described above,a simple pull back mechanism may be utilized to retract the finger. Thisdeployment of the stent will also release the fixation barbs, which willbe shape set to angle away from the device for proper verbal wallengagement.

It is important to note that multiple barbs may be utilized in a well asvarious barb configurations.

Although shown and described is what is believed to be the mostpractical and preferred embodiments, it is apparent that departures fromspecific designs and methods described and shown will suggest themselvesto those skilled in the art and may be used without departing from thespirit and scope of the invention. The present invention is notrestricted to the particular constructions described and illustrated,but should be constructed to cohere with all modifications that may fallwithin the scope for the appended claims.

1. An aneurysm repair system comprising: at least one substantiallycylindrical stent segment, the at least one substantially cylindricalsent segment having modified apexes, the modified apexes including firstsections, second sections and fixation barbs, the second sections beingconfigured to overlap and restrain the fixation barb on an adjacentapex; and graft material affixed, via attachment elements, to at least aportion of the at least one substantially cylindrical stent segment. 2.The aneurysm repair system according to claim 1, wherein the attachmentelements comprise sutures.
 3. The aneurysm repair system according toclaim 1, wherein the substantially cylindrical stent segment comprises asuperelastic material.
 4. The aneurysm repair system according to claim3, wherein the superelastic material comprises a nickel-titanium alloy.5. The aneurysm repair system according to claim 1, wherein thesubstantially cylindrical stent segment comprises a shape memorymaterial.
 6. The aneurysm repair system according to claim 5, whereinthe shape memory material comprises a nickel-titanium alloy.
 7. A stentcomprising at least one substantially cylindrical stent segment havingmodified apexes, the modified apexes including first sections, secondsections and fixation barbs, the second sections being configured tooverlap and restrain the fixation barb on an adjacent apex.
 8. The stentaccording to claim 7, wherein the modified apex is configured to reducefatigue resistance at the apex.
 9. A stent system comprising: at leastone substantially cyclindrical stent segment having modified apexes, themodified apexes including first sections, second sections and fixationbarbs, the second sections being configured to overlap and restrain thefixation barb on an adjacent apex; and a securing mechanism having atleast one protruding member configured for placement in at least one ofthe second sections and a hold down member connected on one end to theat least one protruding member and on the other end to a pull backmember.